The present invention relates generally to a method of producing a plastic component, and in particular a fuel tank for a motor vehicle in which primary shell parts are produced from plastic by the injection-molding process, and in which abutting weld edges of the shell parts are heated and pressed together with one another for welding. The invention also concerns a fuel tank for a motor vehicle having a plurality of shell parts produced from plastic by the injection-molding process and welded with one another.
There has become known in practice a method of producing a plastic component designed as a fuel tank in which the shell parts of the fuel tank each have a peripheral, planar weld edge. Components to be arranged in the fuel tank, such as a surge chamber or baffle elements for example, can be produced by the injection-molding process on the inner side of the shell parts or be fastened thereupon before welding the shell parts. For welding by their weld edges, the shell parts are each pressed onto a heated plate, until the plastic melts. The shell parts are subsequently pressed together by their weld edges.
A disadvantage of the known method is that, for reliable welding that provides a fuel-resistant seal, the shell parts require very wide weld edges and particularly high pressures for pressing the weld edges. Therefore, the plastic component produced by this method has very high tolerances.
Therefore, there is a need for a method for producing a plastic component in such a way that it makes it possible for very close tolerances of the plastic component to be maintained. Furthermore, there is a need for a plastic container which provides a reliable seal and is of a precise shape.
Other needs will become apparent upon a further reading of the following detailed description taken in conjunction with the drawings.
The aforementioned needs are fulfilled according to the present invention by producing a plastic container having, shell parts with weld edge projections pointing toward the respectively opposite shell part and by heating the flanks of the projections of two weld edges to be connected to one another.
By devising the method in this way, the shell parts are heated in a region of the weld edges other than the region where they perpendicularly abut. As a result, the shape of the plastic molding can be fixed by the non-heated regions of the weld edges or by overlapping regions of the projections being pressed against one another. The plastic component produced by the method according to the invention can therefore be produced with particularly close tolerances.
According to an advantageous development, the projections can be shaped in virtually any way desired if the projections are produced by the injection-molding process. As a result, the projections of mutually opposite weld edges can engage in one another, for example in a labyrinthal manner.
Plastic components produced by the known method can have only simple geometrical shapes because of the planar shape of the weld edges. According to another advantageous development of the invention, the weld edges can, for example, be shaped such that they bend from a horizontal plane into a vertical plane when the flanks of the projections are made to begin melting by a heating element arranged between the weld edges. The heating element may subsequently remain in the wall of the fuel tank. As a result, the heating element can, moreover, be arranged reliably in its intended position in the weld edge. The heating element may be designed, for example, as one or more heating wires lying next to one another. The heating of the heating element may be generated, for example, by electric current, magnetic induction, heat conduction or by micro-oscillations. A further advantage of this method is that it allows regions of the plastic parts to which access is difficult to be welded easily.
The method according to the invention makes possible a particularly cost-effective production of the plastic component if the heating element is placed into an injection mold for at least one of the shell parts, in the region of the weld edge, and if the plastic for the shell parts is subsequently introduced into the injection mold.
The method according to the invention can be carried out particularly easily and quickly if the shell parts are pressed together and the heating element is subsequently heated. The heating element reliably begins to melt the plastic at points precisely intended for this purpose in mutually opposite regions of the weld edges. This allows regions in which the shell parts are welded to one another to be fixed very exactly, and regions of the weld edges forming spacers for the intended shape of the plastic component to remain.
With the method according to the invention, a particularly reliable sealing effect of the plastic component designed as a fuel tank can be ensured if the projections of two shell parts to be connected to one another are designed as overlapping butt straps.
The plastic component, designed as a fuel tank and produced by the method according to the invention has particularly close tolerances and high dimensional accuracy if the shell parts are put together in a mold corresponding to the plastic component and if a gas is subsequently introduced into the shell parts and subjected to pressure for the pressing of the shell parts. Heated air, for example, is suitable as the gas.
The method according to the invention requires particularly low expenditure for producing the plastic component with high dimensional accuracy if radially outward-protruding ribs are produced at the weld edges and if a heating element is arranged between the ribs. As a result, the shell parts can be pressed together easily at the ribs using a pair of tongs or two mutually opposite pressure rollers running along the ribs. In this case, the regions of the weld edges next to the ribs stay cold and remain un-deformed during welding.
The additional need of providing a fuel tank having a reliable seal and a precise shape, is fulfilled according to the invention by a heating element being arranged between the shell parts, in the region of the weld edges. Because the heating element can be heated uniformly over its entire length, it is ensured that mutually opposite regions of the shell parts are welded to one other. In the event of a leak, the heating element can be re-heated, until the shell parts of the fuel tank according to the invention are reliably fused with one another. The shape of the fuel tank is in this case changed only insignificantly.
The fuel tank according to the invention is particularly cost-effective if the heating element has at least one heating wire. As a result, the heating element can be heated, for example, by electric current, induction by heat conduction or by micro-oscillations.